The present invention generally relates to an engine combustion condition detecting apparatus equipped with a malfunction (failure) diagnosing apparatus. More specifically, the present invention is directed to such an engine combustion condition detecting apparatus equipped with a malfunction diagnosing apparatus, capable of preventing an erroneous diagnosis of engine combustion conditions caused by malfunctions of this engine combustion condition detecting apparatus.
To detect a combustion condition of an engine, it is important to judge as to whether this combustion condition is under normal condition, or under misfire condition. Conventionally, as an apparatus for detecting a combustion condition, a combustion pressure sensor is used to detect pressure within a combustion chamber. However, since this combustion pressure sensor is expensive, this sensor could not be mounted on each of cylinders due to high cost reason. Accordingly, this combustion pressure sensor is installed only on a specific cylinder to measure combustion pressure thereof. Then, the combustion conditions of the engine are detected by this measured combustion pressure.
Also, to judge an occurrence of misfire in an engine, a torque variation of this engine is acquired as a change in the number of revolutions, and a fluctuation in the engine speed is detected. In this case, an error is produced in the variation of the engine speed unless disturbance is removed based on drive condition. Thus, there is a risk that the fluctuation is erroneously detected.
Under such a circumstance, the following detecting technique has been proposed in which since the combustion conditions within the combustion chambers of the engine are directly detected, the combustion conditions of the engine and the misfire condition are detected. In other words, this conventional detecting technique is performed by measuring the amount of ions contained in the combustion gas within the combustion chambers by way of the ion current detecting means. The combustion conditions of the engine can be directly detected by using this conventional detecting technique without detecting the change of the engine speed, while considering the disturbance and the combustion pressure sensor.
Japanese patent application Un-examined Publication No. JP-A-4-308360 discloses the engine combustion condition detecting apparatus with employment of the above-explained ion current detecting means.
On the other hand, this proposed combustion condition detecting apparatus is arranged by the ion current detecting circuit for detecting the ion currents produced by the combustion within the respective cylinders of the engine, and also the judging means for judging as to whether the internal condition of the cylinder during the ignition operation is under normal combustion, or under misfire condition by using the ion current signal outputted from this ion current detecting circuit. This ion current detecting circuit means is inserted into the conventional ignition circuit. There is no problem when this ion current detecting circuit means is operated under normal condition, namely without under malfunction condition. However, when this circuit is brought into the malfunction condition, even when the ignition operation is performed under normal state, such an erroneous judgement is made in the case that the misfire happens to occur. Moreover, there is another problem that which circuit portion of the ion current detecting circuit means is under malfunction condition.
The present invention has been made to solve the above-described problems, and therefore, has an object to provide a combustion condition detecting apparatus equipped with a malfunction diagnosing apparatus capable of diagnosing malfunction of a detecting apparatus such as an ion current detecting circuit for detecting a combustion condition of an engine in a stage for detecting combustion conditions.
To achieve the above-described object, an engine combustion condition detecting apparatus equipped with a malfunction diagnosing apparatus, according to the present invention, is comprised of: a sensing circuit for sensing an ion current flowing through a combustion room; misfire judging means for judging misfire occurred in the engine in response to the detection signal derived from the sensing circuit; and further malfunction judging means for judging malfunction of the sensing circuit.
Also, as a preferable embodiment of the combustion condition detecting apparatus equipped with the malfunction diagnosing apparatus according to the present invention, when the misfire judging means judges that the misfire happens to occur, the malfunction judging means judges as to whether or not the misfire happens to occur by calculating a variation in revolution numbers for each of cylinders under a predetermined drive condition, whereby the malfunction of the sensing circuit is diagnosed. Furthermore, the malfunction judging means judges malfunction of an element employed in the sensing circuit based upon a mutual relationship between an input signal supplied to the sensing circuit and an output signal derived from the sensing circuit.
Also, as a preferable embodiment of the combustion condition detecting apparatus equipped with the malfunction diagnosing apparatus according to the present invention, the combustion condition detecting circuit is further comprised of monitoring/processing means; when the misfire judging means judges normal combustion, the monitoring/processing means forcibly stops an ignition signal under a predetermined drive condition to thereby induce misfire; the misfire judging means again judges as to whether or not the misfire happens to occur; and the malfunction judging means diagnoses the malfunction of the sensing circuit based on the judgement result of the misfire judging means. Furthermore, the combustion condition detecting circuit is further comprised of monitoring/processing means and external self-diagnosing means; when the misfire judging means judges normal combustion, the monitoring/processing means and the external self-diagnosing means forcibly stop an ignition signal under a predetermined drive condition to thereby induce misfire; the misfire judging means again judges as to whether or not the misfire happens to occur; and the malfunction judging means diagnoses the malfunction of the sensing circuit based on the judgement result of the misfire judging means.
The engine combustion condition detecting apparatus equipped with the malfunction diagnosing apparatus with the above-described arrangement, according to the present invention, is arranged by the malfunction judging means for judging the malfunction of the sensing circuit for detecting the ion currents within the combustion chambers. As a consequence, in such a case that since the sensing circuit is brought into the malfunction condition, the misfire judging means makes the erroneous judgement, the malfunction of the sensing circuit can be correctly detected.
Also, the malfunction judging means acquires both the input signal to the sensing circuit and the output signal from the sensing circuit, and diagnoses the malfunction of the sensing circuit based upon the mutual relationship between the input/output signals. The following malfunction of the circuit elements in the sensing circuit can be individually detected. That is, the charge capacitor, the zener diode, the diode, and the detecting resistor are opened, or shortcircuited.
Furthermore, the engine combustion condition detecting apparatus according to the present invention is further comprised of monitoring/processing means, the monitoring/processing means forcibly stops an ignition signal under a predetermined drive condition to thereby induce misfire. When the misfire judging means judges the normal combustion, the misfire judging means again judges as to whether or not the misfire happens to occur; and the malfunction judging means diagnoses the malfunction of the sensing circuit based on the judgement result of the misfire judging means.
Furthermore, the engine combustion condition detecting apparatus according to the present invention is further comprised of monitoring/processing means and external self-diagnosing means, the monitoring/processing means and the external self-diagnosing means forcibly stop an ignition signal under a predetermined drive condition to thereby induce misfire. When the misfire judging means judges the normal combustion, the misfire judging means again judges as to whether or not the misfire happens to occur; and the malfunction judging means diagnoses the malfunction of the sensing circuit based on the judgement result of the misfire judging means.